drcsim Atlas force torque sensors

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Hi, in which Frame are sensed forces/torques given that are published on the "/atlas/force_torque_sensors" topic? For example the wrench l_hand, is it represented in global frame, frame of pelvis or in the frame of l_arm_mwx?

And why do the handsensors have nonzero values though the hand is not in contact with something?

Thank you